Add musl libc definitions to: src_core_sys_posix_arpa_inet

src/core/sys/posix/arpa/inet.d

@@ -247,6 +247,31 @@ else version( CRuntime_Bionic )
     const(char)*    inet_ntop(int, in void*, char*, size_t);
     int             inet_pton(int, in char*, void*);
 }
+else version( CRuntime_Musl )
+{
+    alias uint16_t in_port_t;
+    alias uint32_t in_addr_t;
+
+    struct in_addr
+    {
+        in_addr_t s_addr;
+    }
+
+    enum INET_ADDRSTRLEN = 16;
+
+    @trusted pure
+    {
+    uint32_t htonl(uint32_t);
+    uint16_t htons(uint16_t);
+    uint32_t ntohl(uint32_t);
+    uint16_t ntohs(uint16_t);
+    }
+
+    in_addr_t       inet_addr(in char*);
+    char*           inet_ntoa(in_addr);
+    const(char)*    inet_ntop(int, in void*, char*, socklen_t);
+    int             inet_pton(int, in char*, void*);
+}
 
 //
 // IPV6 (IP6)